The plant Reynoutria sachalinensis (commonly known as "giant knotweed", and hereinafter more simply referred to as "Reysa") is known to possess agricultural fungicidal activity as evidenced from U.S. Pat. No. 4,863,734 to Pommer et al (the entire content of which is expressly incorporated hereinto by reference). In this regard, it is known that Reysa may be extracted with an organic solvent, such as ethanol, and then subjected to partial evaporation of the ethanol so as to obtain an ethanol extract of Reysa. However, several problems exist when extracting Reysa (or other plant materials) with an organic solvent.
In this regard, when plant materials are extracted with an organic solvent, such as ethanol, the resulting extract includes a complex mixture of materials which vary in terms of water solubilities. The extraction of plant materials can, and often does, result in extracts containing chlorophyll, waxes and oils in addition to more water soluble components. The less water soluble components separate and agglomerate (so-called "tarring out") upon removal of the organic solvent. The extracts and concentrates can also be susceptible to microbial decomposition once the ethanol is removed, thereby leading to inefficacious results.
Broadly, the present invention is embodied in processes to form stable formulations of solvent-extracted Reysa containing minimal (if any) residual organic solvent and to the stable formulations thereby obtained. In particular, the present invention involves subjecting an alcoholic Reysa extract to a primary concentration step (e.g., via distillation, evaporation or the like) to remove a major portion of the organic solvent and to concentrate the Reysa in the resulting primary concentrate solution. Thereafter, an inorganic or organic (e.g., urea) liquid stabilizer is added to the primary concentrate solution which is thereafter subjected to a secondary concentration step so as to remove substantially all (e.g., greater than 95 wt. %) of the organic solvent. In such a manner, therefore, Reysa formulations are provided which are stabilized against microbial decomposition and the resulting reduced inefficacy.